Agarikon

Laricifomes officinalis, long placed in Fomitopsis, is one of the most distinctive perennial polypores of the northern hemisphere. Rather than the flat shelf typical of most brackets, mature specimens elongate downward year after year into a hanging column or beehive shape that can exceed half a metre in length. The whole structure is chalky white to pale yellow, and the outer surface cracks into irregular blocks as it ages.

The fungus is closely tied to old-growth forest. It fruits high on the trunks of large, veteran conifers, generally well above head height, and requires long-standing mature trees with substantial heartwood to complete its slow life cycle. Because such trees have been widely removed across its range, the species is now local and much reduced, and is treated as a conservation priority in parts of Europe.

Its genus name refers to larch, historically the classic support in Europe and Asia, though in western North America it is most often found on Douglas-fir, western larch and hemlock. In all cases the mycelium is a heartwood specialist, working for decades inside a living trunk before the first bracket emerges.

Cap

Young fruiting bodies are rounded white knobs. With age they become hoof-shaped and then markedly elongated, hanging as a soft column or stacked series of tiers 10–60 cm long. The surface is chalky white to cream, ageing pale yellow, buff or grey, and develops deep irregular cracks and concentric furrows that give it a crusted, blocky appearance. Older specimens often carry moss or algae.

Pores

The pore surface is white to cream, ageing yellowish or pale tan, and is smooth in outline with round to slightly angular pores about 3–5 per millimetre. Tube layers are stacked annually, and because the fruiting body extends downward, the layers are visible as a long sequence in vertical section.

Stipe

None. The fruiting body is sessile and attached to the bark by a broad, often narrow point of contact from which the mass hangs — typically high on the bole, sometimes 10 metres or more above the ground.

Flesh & spore print

The context is the key character: soft, chalky and crumbly rather than woody, pure white to cream, and it powders readily when scraped — unusual for a bracket of this size. The spore deposit is white.

Agarikon grows on living and long-dead conifers in old-growth and near-natural forest. In western North America the usual supports are Douglas-fir, western larch, western hemlock, grand fir and occasionally pines and spruces; in Europe and northern Asia it is classically associated with larch. Fruiting bodies form on standing trunks, generally high up, and can persist for decades on the resulting snags.

The range covers the mountains and coastal forests of western North America from Alaska to northern California, together with scattered populations in the Alps, Carpathians, Scandinavia, Siberia and the mountains of central Asia. It is now uncommon almost everywhere, with European populations especially fragmented, and is closely associated with stands that have escaped intensive logging. As a perennial it is present year-round.

The fungus causes an intensive brown rot of conifer heartwood. It removes cellulose from the interior of the trunk while leaving lignin, producing a reddish-brown, cubically cracked residue and eventually hollowing the standing tree from the inside. Because it operates deep in the heartwood, an infected tree can remain alive and full-crowned for many decades while the core is progressively consumed.

Infection is thought to occur through broken branch stubs and wounds high on the trunk, and the interval between colonisation and the appearance of the first bracket may be very long. The hollow trunks that result are prime cavity habitat for owls, swifts, martens and bats, and the fungus's dependence on veteran trees makes it a useful indicator of forest continuity and structural complexity.

Fomitopsis pinicola shares conifer substrates and a white context, but it forms a compact hoof or shelf with a hard, resinous crust banded in red-orange and never elongates into a hanging column; its context is tough and corky rather than chalky and crumbly. Fomes fomentarius has a grey crust and a brown, felty context and grows on hardwoods.

Bridgeoporus nobilissimus, another giant western polypore, forms an enormous, thick, felty-topped bracket at the base of noble and Pacific silver fir, often overgrown with moss — it is basal rather than high on the trunk and has a tough rather than chalky context. Large white Fomitopsis and Climacocystis species may resemble young knobs of Agarikon, but they lack the deeply cracked, elongating, powdery-white structure that develops over successive years.